Add assertion in `produce` method to check buffer capacity in implementations for `BufWriter` #351

Job	Run time
cargo hack check --feature-powerset	51s
cargo hack check --all-targets --feature-powerset	1m 52s
cargo test minimal-versions	1m 12s
cargo test --shallow-minimal-versions	1m 20s
cargo test (stable, i686-pc-windows-msvc, windows-latest)	4m 30s
cargo test (stable, i686-unknown-linux-gnu, ubuntu-latest)	1m 11s
cargo test (stable, x86_64-apple-darwin, macos-latest)	1m 15s
cargo test (stable, x86_64-pc-windows-msvc, windows-latest)	4m 28s
cargo test (stable, x86_64-unknown-linux-gnu, ubuntu-latest)	1m 13s
	17m 52s

Provide feedback